Well Hailminon, you could be crazy like me and refuse to use weaponmans imagine the fun like that. I myself can barely bring myself to log into to just do my daily quests anymore because of the unplayablity of that map.
My real concern. DD1 had this issue on survival mode. I don't know how it was on Xbox but it would lock up my ps3 95% of the time while attempting to get a giraffe. DD2 has it worse. It's the map itself and a map that you are forced to play to advance.
DDA? DD3? Any and I mean any at all unaddressed long running gameplay issues like this will be the end for me.

Well 100mil is a good start for sure. But the fastest/laziest way to ap reset is to just buy your gear right back up and run a c7 map to unlock floor 28. But that ofcourse only really works up until ap 15 or so.
But you can also skip a few and save a bunch if u add in an onslaught map after reset. By leveling up a random set of gear to unlock c7. I believe once you hit ap 7 or 8 you naturally unlock c7. And there's no need to level your gear up.
Disclaimer-- it's been a long time since I was ap<10 so my numbers are probably off by a bit

Floor 150 should be doable with the only trouble being the lag of the lost temple. For every floor that you complete you get 12 levels addes to your minimum. Provided you go above your highest completed floor.
Where you're at now is fine. But what are you looking to do ? Once you start the ap grind it's expensive to stop.
The First 10-15 can go rather fast. If you have the resources and gold you can get burn through them in days.

Chances are yes, you may be wasting your time. Leaderboards are a bit of an after thought. mastery especially. With introduction of mods mastery became much easier. Because of this I don't think the leaderboard gets updated as the game has changed alot since the first week race to complete.

Well for headstrong there's not to much to counter them. Either raw dps kill them before they kill you. Or the new frost weapons can freeze them off a player. That of course requires a 2 player min tho

You have to complete the campaign first. It gives you a quick all be it small tutorial. Once your gear score for your best character breaks 400 you should be able to start c1 expeditions. Adventure is an extension of the campaign sort of. Don't bother with mastery until you have a few of the necessary shards. As far as chaos 8 gear is concerned that's for late game onslaught floors 150+ maybe even 200+. A guide? Sort of we have a few good sources that on can check. Juicebags is definitely one he puts out a lot of updated content on a regular basis. The discord server can be a good place and the wiki itself is currently getting a massive facelift by a team of highly active players with dev support.

I don't use 2 I use 3. I'd use 4 but splitscreen gets rather laggy. It's not just console. PC can do it aswell. As far as the drops are concerned I just finished an ap run from 50-80 not a single 10 mod dropped. The only drop of value I got on that run was a single c8 amp.

For your consideration. In onslaught after a certain floor maybe floor 50 or really any floor above chaos 7. Instead of a campaign, c7 and one random shard. Can we have three random shards instead? After a player reaches a certain point in the game nearly every campaign and c7 shard gets turned to dust as they're generally not needed due to how frequently they are obtained in late game activities.